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Generic Name: methenamine (meh THEH na meen)
Brand Name: Hiprex

Medically reviewed by on June 10, 2019. Written by Cerner Multum.

What is Hiprex?

Hiprex is an antibiotic that is used to prevent recurring bladder infections from coming back. This medicine is used in adults and children at least 6 years old.

Hiprex is usually given after other antibiotics have been given to treat the initial infection.

Hiprex may also be used for purposes not listed in this medication guide.

Important Information

You should not use Hiprex if you have kidney disease, severe liver disease, if you also take a sulfa drug, or if you are dehydrated.

Before taking this medicine

You should not use Hiprex if you are allergic to it, or if you have:

  • kidney disease;

  • severe liver disease;

  • if you also take a sulfa drug; or

  • if you are dehydrated.

Tell your doctor if you have ever had:

  • liver disease;

  • asthma;

  • an allergy to aspirin; or

  • an allergy to yellow food dye.

Hiprex may harm an unborn baby when taken during early pregnancy. It is not known whether Hiprex will harm an unborn baby when taken during the last 3 months of pregnancy. Tell your doctor if you are pregnant or plan to become pregnant.

Tell your doctor if you are breastfeeding.

How should I take Hiprex?

Follow all directions on your prescription label and read all medication guides or instruction sheets. Use the medicine exactly as directed.

Taking more Hiprex than prescribed will not make it more effective, and may cause unwanted side effects (such as bladder irritation, pain, increased urination, and blood in the urine).

You may need to break a tablet in half when giving this medicine to a child.

Drink plenty of liquids while you are taking Hiprex. To make your urine more acidic, your doctor may recommend you drink certain types of liquid (such as cranberry juice) or taking other medicines. Your doctor may also recommend increasing protein in your diet, but avoiding milk or other dairy products. Follow your doctor's instructions very closely.

Use this medicine for the full prescribed length of time, even if your symptoms quickly improve. Skipping doses can increase your risk of infection that is resistant to medication. Hiprex will not treat a viral infection such as the flu or a common cold.

You may need frequent urine tests to determine that an infection has cleared. You may also need blood tests to check your liver function.

Hiprex can affect the results of certain medical tests, especially if you are pregnant while taking this medicine. Tell any doctor who treats you that you are using this medicine.

Store at room temperature away from moisture, heat, and light. Keep the bottle tightly closed when not in use.

Do not share this medicine with another person, even if they have the same symptoms you have.

What happens if I miss a dose?

Take the medicine as soon as you can, but skip the missed dose if it is almost time for your next dose. Do not take two doses at one time.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.

What should I avoid while taking Hiprex?

You may need to follow a special diet while using Hiprex. Follow all instructions of your doctor or dietitian. Learn about the foods to eat or avoid to help control your condition.

Hiprex side effects

Get emergency medical help if you have signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Call your doctor at once if you have:

  • painful urination;

  • increased urination;

  • blood in the urine; or

  • any new or worsening symptom.

Common side effects may include:

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

What other drugs will affect Hiprex?

Other drugs may affect Hiprex, including prescription and over-the-counter medicines, vitamins, and herbal products. Tell your doctor about all your current medicines and any medicine you start or stop using.

Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use this medication only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.